Icosanoic acid

Icosanoic Acid (Arachidic Acid / Eicosanoic Acid): A Comprehensive Reference

1. Identity and Chemical Characterization

Names and Classification

Icosanoic acid is the IUPAC-preferred name for the straight-chain, 20-carbon saturated fatty acid formally designated n-eicosanoic acid. It is catalogued in the LIPID MAPS Structure Database under the identifier LMFA01010020, with the shorthand lipid notation FA 20:0, and carries the synonyms eicosanoic acid, arachidic acid, arachidate, arachic acid, eicosanoate, and n-eicosanoic acid. The compound is most commonly encountered in scientific literature under the name arachidic acid, a designation derived from the Latin arachis, meaning peanut — the oil from which the commercial product is traditionally derived. Its name reflects its occurrence as a minor constituent of peanuts, macadamia nuts, cocoa butter, corn oil, canola oil, and peanut oil.

The compound carries CAS registry number 506-30-9, molecular weight 312.53 g/mol, and EC Number 208-031-3. Its linear molecular formula is CH₃(CH₂)₁₈COOH. It belongs to the class of long-chain saturated fatty acids. In the broader context of saturated fatty acid taxonomy, icosanoic acid (C20:0) is grouped among the very long-chain saturated fatty acids (VLCSFAs), alongside behenic acid (C22:0) and lignoceric acid (C24:0).

Physical and Chemical Properties

Icosanoic acid presents as shining, white crystalline leaflets that are soluble in ether and slightly soluble in water. It is a solid at room temperature with a melting point of 74–76 °C, and is freely soluble in benzene, chloroform, diethyl ether, and petroleum ether, but insoluble in water. It decomposes at approximately 328 °C. As a carboxylic acid, it carries the typical chemical properties of fatty acids, including the ability to react with NaHCO₃ to form salts and with alcohols to form esters.

Relationship to Arachidonic Acid

A frequent source of confusion involves distinguishing icosanoic acid from arachidonic acid (C20:4 n-6), its structurally related but biologically distinct counterpart. The two share a 20-carbon backbone, but icosanoic acid is fully saturated (no double bonds), whereas arachidonic acid contains four double bonds and is an omega-6 polyunsaturated fatty acid (PUFA) with profound signaling roles. Eicosanoic acid can be produced by catalytic hydrogenation of arachidonic acid; arachidonic acid is itself obtained from food or by desaturation and chain elongation of the plant-derived essential fatty acid linoleic acid. The two molecules are therefore metabolically linked but functionally very different.

2. Natural Sources and Distribution

Icosanoic acid is a widely distributed but minor component of the fats of certain edible vegetable oils. It is a minor constituent of butter, perilla oil, peanut oil, corn oil, and cocoa butter. In quantitative terms, it is present in peanut oil at approximately 1.1%–1.7% and in corn oil at approximately 3%. Icosanoic acid occurs naturally in both fish and vegetable oils. It has been identified specifically in peanut butter and in anaerobic fungi.

The commercial product is primarily derived from groundnut (peanut) oil. Beyond food oils, icosanoic acid is also found as a component of propolis — the resinous mixture produced by honeybees — where it occurs as both free acid and esterified forms such as the ethyl ester. The ethyl ester of arachic acid has been isolated and characterized from Cameroonian propolis by chromatography of ethanolic extracts and identified by nuclear magnetic resonance (NMR) spectra.

From a metabolic perspective, icosanoic acid is also produced endogenously in humans. In addition to its dietary origin, it has been established that endogenous production contributes to circulating VLCSFA concentrations, and dietary intake or overall healthier lifestyle factors may further influence those concentrations.

3. Common Forms and Preparations

In commercial and research contexts, icosanoic acid is available in several forms:

• Free fatty acid: It appears as a white to almost white powder or crystal, available at purities exceeding 98.0% by gas chromatography (GC).
• Methyl and ethyl esters: Methyl arachidate and ethyl arachidate are standard derivatives used in analytical and biochemical research. The ethyl ester (arachic acid ethyl ester, AAEE), with the formula C₂₂H₄₄O₂, is also an isolated natural compound found in propolis.
• Dietary form in whole foods: Icosanoic acid is consumed as a natural minor component of peanuts, macadamia nuts, and various plant oils, where it is typically esterified within triacylglycerols and phospholipids.
• Industrial preparations: Arachidic acid is used in the manufacture of pharmaceuticals, soaps, cosmetics, and food packaging because of its surfactant-like properties. It is also utilized in organic synthesis, lubricating greases, waxes, and plastics.

There is currently no standardized isolate of icosanoic acid marketed as a primary standalone dietary supplement in the manner of, for example, omega-3 fatty acid capsules. Its occurrence in the supplement context is as a naturally occurring trace constituent within peanut-derived products, nut oils, and propolis preparations.

4. Traditional and Historical Use

Icosanoic acid per se was not recognized as a discrete entity until the development of analytical chemistry; its natural sources, however, have long histories of traditional use across many cultures. Because the compound cannot be isolated by premodern techniques, all historical and traditional use attributable to it is necessarily embedded within the use of its source materials.

• Peanuts (Arachis hypogaea): Cultivated for at least 7,500–8,000 years in South America, peanuts spread globally through colonial trade and have been used as food, as a source of topical oil, and as traditional remedies across African, Asian, and American cultures.
• Propolis: Propolis is a natural resinous mixture of botanical balsams and resins combined with digestive enzymes of bees, collected by honeybees (Apis mellifera) from various plant sources. Its medicinal use dates back to ancient Egypt, Greece, and Rome, where it was applied to wounds, used as an antibacterial agent, and consumed for general health. Natural products like propolis have been traditionally used in the treatment of pain. The identification of arachic acid ethyl ester as a bioactive propolis constituent helps justify the traditional use of propolis in the treatment of pain.
• Cocoa butter: Used by Mesoamerican civilizations for millennia in food and topical preparations, cocoa butter contains icosanoic acid as a minor fatty acid component.

It must be emphasized that historical practitioners were using complex matrices rather than isolated icosanoic acid, and attributing specific traditional effects to this single constituent involves an anachronistic projection not supported by pre-modern medical texts.

5. Key Constituents, Biochemistry, and Established Mechanisms

Structural Role in Membranes

Because of its structural role in lipids, icosanoic acid may influence membrane fluidity and signaling, although these functions are less well characterized compared with essential polyunsaturated fatty acids. As a fully saturated fatty acid, icosanoic acid straightens the acyl chain region of phospholipid bilayers, a property relevant to membrane rigidity and the organization of lipid microdomains.

Role in Sphingolipid and Ceramide Biology

Because VLCSFAs are components of ceramides involved in apoptosis, there is strong evidence that VLCSFAs are protective against apoptosis and cell death. Ceramides are a structurally heterogeneous and complex group of sphingolipids containing derivatives of sphingosine bases in amide linkage with a variety of fatty acids. Ceramides may play an essential role in structuring and maintaining the water permeability barrier function of the skin, and in conjunction with other corneum lipids, form ordered structures. Very long-chain fatty acids including icosanoic acid serve as the fatty acid acyl moieties in specific ceramide species that contribute to both skin barrier integrity and neurological membrane composition.

Distinction from Arachidonic Acid Metabolic Pathways

Arachidonic acid (the polyunsaturated C20:4 isomer) is the direct precursor of bioactive lipid metabolites including eicosanoids such as prostaglandins, leukotrienes, and epoxyeicosatrienoic acid obtained from three distinct enzymatic metabolic pathways: the cyclooxygenase pathway, lipoxygenase pathway, and cytochrome P450 pathway. Icosanoic acid (C20:0), being fully saturated, is not a substrate for these eicosanoid-generating enzymes and does not serve as a direct precursor to prostaglandins or leukotrienes through these pathways. Its biological activity therefore derives from different mechanisms — structural membrane roles, ceramide incorporation, and its identity as a biomarker of dietary and metabolic status.

Circulating Levels as Biomarkers

Circulating icosanoic acid and related VLCSFAs may serve as integrated biomarkers of diet and metabolism rather than direct effectors of health. In addition to its dietary origins, endogenous production contributes to circulating VLCSFA concentrations, and dietary intake or an overall healthier lifestyle may further influence those levels.

6. Scientific Evidence by Area of Use

6.1 Cardiovascular Health

The most extensively investigated area of health association for circulating icosanoic acid (C20:0) is cardiovascular disease. Research is observational and epidemiological in nature; to date, no randomized controlled trials have specifically supplemented isolated icosanoic acid to evaluate cardiovascular outcomes.

A community-based cohort study investigated associations between circulating VLCSFAs and cardiovascular health, including 2,198 adults without carotid artery plaques (CAPs) at baseline, measuring the percentage of erythrocyte VLCSFAs including arachidic acid (C20:0), behenic acid (C22:0), and lignoceric acid (C24:0) by gas chromatography. The presence of CAPs was determined at baseline and every three years thereafter by ultrasound examination; a meta-analysis was also conducted to summarize pooled associations between circulating VLCSFAs and the risk of cardiovascular diseases. During a median of 7.2 years of follow-up, 573 women and 281 men were identified as CAP incident cases. VLCSFAs were inversely related with CAP risk in women (all p-trend <0.05) but not in men. Multivariate adjusted hazard ratios for the highest versus lowest quartile were 0.80 (95% CI: 0.63–1.01) for C20:0 in women.

The pooled hazard ratios from seven studies including 8,592 participants and 3,172 CVD events were 0.67 (95% CI: 0.57–0.79) for C20:0, 0.66 (0.48–0.90) for C22:0, and 0.57 (0.42–0.79) for C24:0, respectively — all indicating an inverse association of higher circulating VLCSFA levels with cardiovascular disease risk.

A 2025 nested case-cohort analysis within the European Prospective Investigation into Cancer and Nutrition (EPIC-Potsdam) cohort further examined this question. Researchers investigated prospective associations of circulating VLCSFAs (C20:0, C22:0, C24:0) across multiple plasma lipid classes with type 2 diabetes (T2D) and cardiovascular disease (CVD), constructing two nested case-cohort studies: one with 1,911 participants and 774 T2D cases, and one with 1,704 participants and 547 CVD cases. The study highlighted that VLCSFA associations with disease depend on the specific lipid classes carrying them, cautioning against treating saturated fats as a single uniform group and suggesting that lipid class-specific VLCSFA measures could enhance risk assessment and prevention strategies.

Several meta-analyses suggest a beneficial association of VLCSFAs with cardiovascular health outcomes as well as lower risks of type 2 diabetes, atrial fibrillation, heart failure, and coronary disease.

Evidence strength: Observational and meta-analytic data are consistent in showing an inverse association between circulating icosanoic acid levels and cardiovascular disease risk. However, VLCSFAs may influence cardiometabolic health differently from other saturated fatty acids, though evidence remains inconclusive partly because VLCSFAs are metabolically derived from SFA, making it difficult to disentangle their individual effects due to potential confounding of correlated lipids. No controlled supplementation trials with isolated icosanoic acid have been conducted.

6.2 Type 2 Diabetes Risk

Several studies have found that elevated levels of icosanoic acid in erythrocytes and systemically are associated with a lower risk for type 2 diabetes; however, the mechanistic details of this association are at present not well understood, and more research is needed.

Research on the effects of arachidic, behenic, and lignoceric acid on type 2 diabetes has not yielded consistent results. In one nutritional intervention, significantly higher plasma concentrations of total VLCSFAs, arachidic, behenic, and lignoceric acids were observed after peanut and peanut butter interventions compared to baseline. The beneficial properties of these VLCSFAs in the context of T2D have not been extensively investigated.

Evidence strength: Preliminary and inconsistent. Most evidence is observational, with confounding by overall dietary pattern unresolved. No interventional trials directly targeting icosanoic acid and glycemic control have been reported.

6.3 Anti-Inflammatory and Analgesic Activity

Research on the anti-inflammatory and analgesic properties of icosanoic acid has focused specifically on its ethyl ester derivative isolated from propolis. The objective of one published study was to evaluate the anti-inflammatory and analgesic activities of the ethyl ester of arachic acid, a compound isolated from Cameroonian propolis by chromatographic separation of ethanolic extracts.

The anti-inflammatory and analgesic properties of oral administration of arachic acid ethyl ester were evaluated using carrageenan-induced paw edema, xylene-induced ear edema, cotton pellet-induced granuloma formation, and hot plate test in rats at doses of 12.5, 25.0, and 50.0 mg/kg body weight. Arachic acid ethyl ester produced maximum inhibition at 50.0 mg/kg for carrageenan-induced paw edema (62.5%), xylene-induced ear edema (54.5%), and cotton pellet-induced granuloma (47.4%), and increased mean latency in the hot plate test in rats, indicating both acute and chronic anti-inflammatory properties as well as central analgesic properties.

Evidence strength: Preclinical only (animal models). No human clinical trials have tested icosanoic acid or its ethyl ester for anti-inflammatory or analgesic outcomes. Results cannot be extrapolated to human dosing or therapeutic use.

6.4 Influence on Circulating Lipid Levels — Diet and Lifestyle Interactions

A systematic review registered on PROSPERO (ID: CRD42021233550) searched MEDLINE, EMBASE, and the Cochrane databases up to February 2022, identifying a total of 12 studies consisting mostly of cross-sectional analyses, which documented associations of dietary intake with total plasma or red blood cell VLCSFAs. Two cross-sectional analyses showed a consistent positive association between total fat and peanut intake with C22:0 and C24:0 and an inverse association between alcohol intake and C20:0 and C22:0. A moderate positive association between physical activity and C22:0 and C24:0 was also observed. Results on the effects of smoking on VLCSFAs were conflicting.

Physical activity also increased VLCSFA levels, although not to the same extent as diet. These studies suggest that generally healthier lifestyle habits may improve cardiometabolic health by increasing the circulating levels of VLCSFAs, including icosanoic acid.

In a nutritional trial, peanut and peanut butter intervention significantly elevated plasma concentrations of arachidic, behenic, and lignoceric acids compared to baseline (p < 0.05). These results were consistent with a similar trial where peanut butter intake led to higher plasma concentrations of behenic and lignoceric acid after 2–8 hours of consumption.

6.5 Cognitive and Neurological Associations

VLCSFAs may also be important in neural development and cognition. However, specific clinical evidence attributing neurological benefits directly to icosanoic acid in human subjects is not currently available in the peer-reviewed literature. The association is derived from VLCSFAs' known role as structural components of brain ceramides and sphingolipids.

6.6 Skin and Dermatological Applications

Icosanoic acid's role in skin biology is indirect, mediated through its presence in ceramide molecules. The surface of human skin is protected by corneocytes that maintain skin elasticity by binding to the double-chained lamellar structure of ceramides, which are abundantly present in the stratum corneum. Ceramides are arranged in parallel as a layered structure, with moisture maintained between layers, providing an overall barrier function. Abnormal ceramide levels are commonly observed in atopic eczema, dermatitis, and psoriasis. Because very long-chain fatty acids including icosanoic acid serve as acyl moieties in specific ceramide species, changes in their availability may theoretically affect skin barrier function. However, this connection has not been demonstrated in clinical trials using icosanoic acid supplementation.

In cosmetics, icosanoic acid is incorporated into cosmetic products for its emollient properties.

7. Body Systems and Health Areas of Association

• Cardiovascular system: Higher circulating C20:0 is inversely associated with carotid artery plaques, heart failure, atrial fibrillation, and coronary heart disease in observational data and meta-analyses.
• Metabolic/endocrine: Circulating C20:0 is inversely associated with type 2 diabetes incidence in several observational cohorts, though evidence is inconsistent.
• Integumentary system (skin): Structural role as a ceramide acyl component involved in skin barrier function; used topically as an emollient in cosmetic formulations.
• Nervous system: Potential role in neural membrane composition via ceramide and sphingolipid pathways; associations with cognition are described in the VLCSFA literature but are not substantiated by human intervention trials.
• Inflammatory pathways: Preclinical evidence from animal models suggests anti-inflammatory and analgesic properties of icosanoic acid ethyl ester; no human data exist.

8. Dosage Forms and Reported Study Dosages

The only reported experimental dosing range for a form of icosanoic acid in a biological efficacy study is oral administration of arachic acid ethyl ester at 12.5, 25.0, and 50.0 mg/kg body weight, tested in rats using inflammation and pain models. No human clinical dosing studies have been published for isolated icosanoic acid or its ester derivatives as a supplement.

In the context of food-based interventions, significantly higher plasma concentrations of arachidic acid and total VLCSFAs were observed after whole peanut and peanut butter dietary interventions compared to baseline, though specific doses of icosanoic acid delivered were not reported as primary outcome variables.

There is no specific Tolerable Upper Intake Level established for icosanoic acid itself. No regulatory body has issued a specific daily reference intake or tolerable upper limit for icosanoic acid as a standalone nutrient.

9. Safety Considerations and Interactions

General Toxicological Profile

Icosanoic acid belongs to the category of n-alkyl carboxylic acids, which as a group demonstrate low acute oral, dermal, and inhalation toxicity; low potential to cause skin sensitization; low repeated-dose toxicity; and low or no reproductive or developmental toxicity, as classified by the U.S. EPA's Chemical Assessment and Management Program (ChAMP). In concentrated form, it is identified as a skin and strong eye irritant.

Cardiovascular Context — Saturated Fat Caveats

A nuanced consideration applies to the broader saturated fat context. While circulating icosanoic acid as a biomarker shows inverse associations with cardiovascular risk, the relationship between dietary saturated fat intake and cardiovascular health is a separate and more complex question. Higher saturated fat intake overall is generally associated with elevated LDL cholesterol levels and cardiovascular risk in controlled feeding studies. The distinction between different saturated fatty acids is an active area of research, but current evidence does not support specific health claims for arachidic acid intake beyond its role in contributing to overall dietary fat.

Emerging evidence shows that not all saturated fatty acids affect cardiometabolic health equally, as their effects may vary depending on chemical structure. The specific effect of icosanoic acid intake — distinct from the general effect of total dietary saturated fat — on LDL cholesterol or cardiovascular risk has not been determined in controlled human trials.

Dietary Fat and Medication Interactions

There are no specific drug interactions identified for icosanoic acid itself. However, dietary saturated fat intake can influence lipid-lowering medications such as statins indirectly by affecting lipid profiles; high saturated fat intake may attenuate their lipid-lowering effect. This caveat applies at the level of total dietary saturated fat, not icosanoic acid specifically.

Peanut Allergy

Icosanoic acid in most dietary contexts is consumed as part of peanut or peanut-derived products. Individuals with peanut allergy must be aware that any peanut-derived supplement or oil may carry allergen risk. This is a consideration of the source material, not of icosanoic acid itself, as the fatty acid per se is not allergenic.

Evidence Gaps and Research Limitations

Although most observational studies examining lifestyle determinants of VLCSFAs have low risk of bias, findings are limited by the bivariate analyses presented in the majority of included studies, making the impact of confounding unclear. Evidence on VLCSFAs remains inconclusive partly because they are metabolically derived from other saturated fatty acids, making it difficult to disentangle their individual effects due to potential confounding by correlated lipids. The field currently lacks randomized controlled trials isolating the effect of icosanoic acid supplementation on any health outcome in humans.

References

• LIPID MAPS Structure Database — Icosanoic Acid (LMFA01010020)
• PubChem — Eicosanoic Acid (CID 10467), National Institutes of Health
• Very long-chain saturated fatty acids in plasma lipids: association with cardiometabolic risk influenced by lipid interactions — PMC 2025
• Circulating Very-Long-Chain Saturated Fatty Acids Were Inversely Associated with Cardiovascular Health: A Prospective Cohort Study and Meta-Analysis — Nutrients 2020
• Lifestyle Factors Associated with Circulating Very Long-Chain Saturated Fatty Acids in Humans: A Systematic Review of Observational Studies — PMC 2023
• Anti-Inflammatory and Analgesic Effect of Arachic Acid Ethyl Ester Isolated from Propolis — PMC 2020
• Effect of Crushing Peanuts on Fatty Acid and Phenolic Bioaccessibility: A Long-Term Study — PMC 2022
• Arachidonic acid metabolism in health and disease — PMC 2023
• Arachidic Acid — Metabolon Metabolite Reference
• Arachidic Acid (SFA 20:0): Sources and Dietary Role — FoodContents.com
• Arachidic Acid — Haz-Map Hazardous Agents Database (citing Merck Index and EPA ChAMP)
• Arachidic Acid (CAS 506-30-9) — ChemicalBook